The T-cell receptor is essential for major functions of the adaptive immune system and is one of the most complex cell surface receptors. It is composed of eight polypeptide chains that must be assembled in the ER in the proper stoichiometry for it to perform its vital functions. As such, its assembly poses a formidable task for the ER quality control machinery. Although a large body of literature exists on the assembly and quality control of the TCR, these efforts have focused primarily on the unusual transmembrane domains of the individual chains. These possess charged residues that, when unpaired, accelerate degradation of the TCR chains and are believed to drive assembly. However, the basis of this presumed integral membrane quality control step has not been elucidated. Furthermore, very little attention has been directed to possible roles for the lumenal portions of this receptor, which are likely to be the regions scrutinized by the known quality control machinery of the ER. To remedy this deficiency, we propose to combine biophysical and cell based studies to obtain high resolution structural and kinetic data on the folding and assembly of the TCR that can be correlated with checkpoints in the cell. Our preliminary data obtained from these approaches have already revealed two unanticipated features of the TCR -chain. We find that its constant domain is unstructured in the absence of association with the - chain and that its transmembrane region is not integrated into the ER membrane when expressed alone. These two features are very likely to provide checkpoints in the quality control of receptor assembly. These preliminary insights will be expanded in order to obtain an integrated view of the ER mechanisms that aid and monitor TCR biosynthesis allowing only properly assembled receptors to be expressed on the cell surface.